The dominance of iOS will be challenged later this year as Android hurdles toward becoming the most-used mobile operating system on tablets, according to IDC. The researcher has updated its forecast to reflect the surging interest in slates such as the Nexus 7 that are smaller and cheaper than Apple's iPads, with the latest data projecting shipments of 190.9 million units in 2013, up from the previously expected 172.4 million.

The group notes that half of the tablets shipped this quarter had screens smaller than eight inches. IDC analyst Jitesh Ubrani believes this suggests that consumers are realizing smaller slates are often better suited for typical usage than the larger options. Vendors are reportedly racing to meet that demand and most of them will offer Android devices, which should allow Google's platform to overtake iOS before the year is up.

Android tablets captured a healthy slice of the market in 2012 and its share is due to reach 48.8% in 2013, up from 41.5% in IDC's previous forecast. When that happens, iOS will purportedly slip from 51% of the market in 2012 to 46% in 2013. And while Android is chipping away at iOS, IDC says Windows will be nipping at both their ankles as it's expected to grow from 1% of the market last year to 7.4% in 2017. The researcher doesn't have high hopes for Windows RT, however, as its growth is estimated to remain below 3% over the next five years.

"Microsoft's decision to push two different tablet operating systems, Windows 8 and Windows RT, has yielded poor results in the market so far," said analyst Tom Mainelli. "Consumers aren't buying Windows RT's value proposition, and long term we think Microsoft and its partners would be better served by focusing their attention on improving Windows 8. Such a focus could drive better share growth in the tablet category down the road."